1. Field of Invention
The present invention relates generally to the field of carbon electrode cleaning, and more particularly to the cleaning of spent frame mounted carbon butts following an aluminum smelting process.
2. Technical Background
Aluminum smelting is a chemical reduction process which converts alumina (aluminum oxide) into aluminum and oxygen. The reduction process is typically preformed in a large reduction cell that includes a carbon lined container or xe2x80x9cpotxe2x80x9d at least partially filled with a molten mixture of alumina dissolved in cryolite and other materials such as fluorides. The carbon lined steel pot forms the cathode while a plurality of frame mounted carbon blocks suspended in the bath form the associated anodes.
During smelting, a voltage potential is applied between the carbon anodes and the pot, resulting in a large current flow from the anodes through the molten bath mixture to the cathode. The electrical current passing through the bath reduces the alumina into its aluminum and oxygen components, which results in the aluminum ions falling from the mixture to the bottom of the pot and oxygen ions reacting with the carbon provided by the carbon blocks to form CO and CO2. Thus, while aluminum is being formed, the carbon blocks are slowly being consumed over time due to the ongoing chemical reaction of the oxygen with the carbon. Generally, these waste gasses are vented from the pot and the non-suspended aluminum is periodically evacuated from the cell. Over time, this reaction necessitates the replacement of the spent anodes in order to maintain adequate production levels of aluminum.
A by-product of the above-described reaction is the formation of a hardened crust atop the cell. The crust is predominantly formed of cryolite, which over time, begins to accumulate on the carbon blocks and their associated support stubs. Thus, when the anodes are removed from the bath, the remaining carbon remnants or butts supported on the frame of the anodes are substantially covered by a hardened encrustation of cryolite, which until removed, prevents reuse of the remaining carbon butts. Because recycled carbon seasoned by aluminum smelting is preferable to non-seasoned carbon for new or replacement carbon anodes used in aluminum smelting, aluminum manufacturers favor removal of the cryolite encrustation from the spent carbon anodes over disposal of the encrusted anodes as carbon butts can be recycled and reused to make new carbon blocks for later use in the smelting process.
Heretofore, several methods have been employed to remove the cryolite encrustation from the carbon anodes. One such method involves a combination of manually hammering and scrapping the anode to substantially remove the hardened encrustation. Another method employs powered scraping arms, which act upon the cryolite. Still another method employs a vibrating scraping tool. Each of these methods, however, are labor intensive, time consuming, and are generally viewed by the industry as too slow to keep pace with aluminum smelting plants. As many smelting plants typically manufacture their own electrodes as a companion function to smelting, the electrode manufacturing process must keep in step with the smelting process. Accordingly, anode cleaning processes must adhere to strict time guidelines in order to provide the requisite number of cleaned carbon butts desired for new or replacement carbon anode manufacture.
In addition, due to technological advances in reduction cell operation, aluminum smelting plants can now add heavier blankets of alumina to the production cell, which in turn fosters the formation of a thicker and denser crust atop the reduction cell and thus provides for greater heat retention. While this is preferable for increased aluminum output, these advances have resulted in the formation of harder and denser cryolite encrustation formed on the spent anodes.
Accordingly, there is a need for an approved carbon electrode cleaning system and method capable of disengaging these harder cryolite encrustations from the anode frames and carbon butts. More specifically, there is a need for a cleaning system that substantially conforms to the shape of typical carbon butts that remain affixed to the stubs of the anodes so that the encrustation can be removed without additional labor intensive and time consuming manual cleaning operations. Such a device should be simple to use, consistent in operation, and capable of keeping pace with modern smelting and carbon anode reclamation processes preformed at aluminum processing plants. It is to the provision of such a system and method that the present invention is primarily directed.
One aspect of the present invention relates to a method of cleaning a spent carbon anode, the spent carbon anode including a carbon butt, a frame having a yolk and stub for supporting the carbon butt, and an encrustation affixed to the spent carbon anode. The method includes the steps of urging a plow blade into and through the encrustation such that the plow blade passes between the frame and carbon butt to disengage a significant portion of the encrustation from the spent carbon anode. The method further includes the step of rotationally engaging the frame and carbon butt with first flailing elements rotating in a first plane with respect to the spent carbon anode to abrade additional encrustation from the spent carbon anode. The frame and carbon butt are also rotationally engaged by second flailing elements rotating in a second plane with respect to the spent carbon anode to further abrade additional encrustation from the spent carbon anode. Rotation of the flailing elements in the second plane is substantially orthogonal to rotation of the flailing elements in the first plane.
In another aspect, the present invention is directed to a system for cleaning a spent carbon anode. The spent carbon anode includes a carbon butt, a frame including a yolk and stub for supporting the carbon butt, and an encrustation affixed to the spent carbon anode. The system includes a conveyer for transporting the spent carbon anode, and a first station communicating with the conveyer to receive and engage the spent carbon anode. The first station includes a plow assembly having a laterally extendable plow blade constructed and arranged to dislodge a significant portion of the encrustation from the spent carbon anode as the plow blade is extended through the spent carbon anode between the carbon butt and the frame. A second station communicating with the conveyer downstream of the first station receives the spent carbon anode conveyed from the first station. The second station includes a first rotatable flailing assembly having first flailing elements constructed and arranged to rotatably engage the spent carbon anode in a first plane to abrade additional encrustation from the spent carbon anode. A third station communicates with the conveyer downstream of the second station to receive the spent carbon anode conveyed from the second station. The third station includes a second rotatable flailing assembly having second flailing elements constructed and arranged to rotatably engage the spent carbon anode in a second plane to abrade additional encrustation from the spent carbon anode. Again, rotation in the second plane is substantially orthogonal to rotation in the first plane.
An additional aspect of the present invention relates to an apparatus for removing an encrustation from a spent carbon anode having a carbon butt defining at least one concave groove on its upper surface, and a frame having a yolk and stub for supporting the carbon butt. The apparatus comprises a drive motor, a shaft rotatably coupled to the drive motor, and an elongated flailing element affixed to the shaft at a location remote from the drive motor. The elongated flailing element is constructed and arranged to substantially conform to the shape of the concave groove defined in the upper surface of the carbon butt upon rotation of the shaft.
Yet another aspect of the present invention is directed to an apparatus for removing an encrustation from a spent carbon anode including a carbon butt defining at least one concave groove on its upper surface and a frame having a yolk and stub for supporting the carbon butt. The apparatus includes a drive motor, a plow beam extendably coupled to the drive motor, and a plow blade affixed to an end of the plow beam remote from the drive motor. The plow blade includes a blade extension that is sized and shaped to substantially conform to the shape of the concave groove, and is adapted to dislodge a substantial portion of the encrustation from the concave groove upon extension of the plow beam.
The improved carbon electrode cleaning system and method of the present invention results in a number of advantages over other devices and methods known in the art. For example, the improved plow blade of the present invention is sized and shaped to engage the encrustation at the crust line adjacent the upper surface of the carbon butt within the concave groove defined thereon. Rapid disengagement of the encrustation from the carbon butt is thus facilitated enabling the plow blade to pass through the entire length of the spent carbon anode in a single stroke. Other devices lacking this feature, have been known to stall at some point during the initial stroke.
Additionally, the use of the dual directional flailing assemblies in accordance with the present invention provides substantially more scrubbing of the spent carbon anode surface area in a much shorter period of time than other systems and methods presently known in the art. As a result, the yolk, stubs, and carbon butt of the spent carbon anodes carry far less residual encrustation following cleaning in accordance with the present invention.
Moreover, the unique curvilinear orbital path of the flailing elements of one embodiment of the flailing assemblies of the present invention enable the flailing assembly to be laterally inserted between the yolk, stubs and upper surface of the carbon butt. The construction and arrangement of these flailing elements further facilitate cleaning of the concave groove defined within the upper surface of the carbon butt, as the flailing elements substantially conform to the shape of the concave groove. Accordingly, manually manipulated tools are no longer necessary for carbon butt groove cleaning.
Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from the description or recognized by practicing the invention as described herein.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide further understanding of the invention, illustrate various embodiments of the invention, and together with the description, serve to explain the principles and operation of the invention.